The following is a comprehensive analysis of the influencing factors of the concrete elastic modulus tester, which is carried out from the dimensions of equipment performance, specimen preparation, testing process, and environmental conditions, aiming to reveal key control points to ensure measurement accuracy:

1、 Performance parameters of instruments and equipment

Core component accuracy

Load sensor: Nonlinear error should be<± 0.5% FS, and zero drift caused by long-term creep will be directly superimposed on the strain reading;

Resolution of displacement sensor: Insufficient micrometer level accuracy will amplify small displacement errors during the elastic deformation stage. It is recommended to use LVDT linear variable differential transformer;

Stability of loading rate: If the hydraulic servo system experiences pulsating oil supply, it will cause stress rate fluctuations of>± 2%, which will disrupt the quasi-static loading conditions.

Typical fault: Pressure rings that are not regularly calibrated are prone to producing hysteresis loops, causing the unloading curve to deviate from the theoretical path and artificially increasing the residual deformation ratio.

2、 Preparation and pretreatment process of specimens

Geometric dimension control

End face flatness: When the parallelism deviation of the upper and lower surfaces of the specimen is greater than 0.02mm, eccentric compression will occur, causing secondary bending moments to change the true stress distribution;

Quality density difference: For every 1% increase in internal porosity caused by insufficient compaction, the measured elastic modulus can decrease by 3% -5%;

Consistency of maintenance: Fluctuations in standard maintenance room temperature and humidity (Δ T>2 ℃/Δ RH>5%) can cause a difference of up to 8% in cement hydration degree, significantly affecting early elastic modulus development.

Optimization plan: Adopt intelligent vibration system to control the forming density, and apply release agent on the inner wall of the trial mold to reduce friction resistance.

3、 Key control nodes in the testing process

Alignment and preloading treatment

Physical alignment accuracy: When the deviation between the axis of the specimen and the center of the pressure plate is greater than 1mm, the local pressure bearing area of the contact surface decreases, resulting in shear component interference with axial deformation;

Pre load elimination gap: Without applying initial load (about 5% of the ultimate load), entering the formal loading stage directly, the false deformation caused by the machine's idle stroke can account for up to 15% of the total deformation.

Loading system execution

Graded loading strategy: Load in 4-5 levels according to the requirements of GB/T 50081, and creep deformation cannot be released if the holding time is less than 60 seconds;

Cycle number control: After repeated preloading three times, formal testing can effectively close microcracks and stabilize the contact state.

4、 Disturbance effects of environmental conditions

Temperature humidity coupling effect

Temperature sensitivity: For every 1 ℃ increase in temperature, the volume expansion coefficient of concrete is about 1 × 10 ⁻⁵, which is equivalent to introducing additional strain;

Humidity dependence: The dry environment promotes the escape of moisture, causing the specimen to self shrink. During the testing period, the relative humidity should be controlled at 60% ± 5%.

Vibration isolation requirements

Basic vibration reduction configuration: When the ground vibration acceleration in the laboratory is greater than 0.05g, an airbag isolation platform needs to be set up, otherwise the environmental vibration will be captured by the displacement meter as a pseudo deformation signal.

5、 Human operation and data processing

Subjective judgment error

Visual interpretation deviation: When manually observing the initial zero point, the pupil resolution limit is about 0.1mm. It is recommended to use the automatic zero finding function instead;

Data truncation interval: Incorrect selection of plastic section instead of elastic section, resulting in secant modulus replacing tangent modulus, with a numerical deviation of up to 20%.

Applicability of computational models

Selection of constitutive relationship: Directly adopt the Euler Bernoulli beam theory to assume a uniform strain field, ignoring the edge effect correction term caused by shear hysteresis effect.

The accuracy of the concrete elastic modulus tester is influenced by multidimensional factors such as equipment hardware performance, specimen processing quality, testing process standardization, environmental control level, and personnel proficiency. Establishing standardized operating procedures (SOP), implementing equipment preventive maintenance (PM), and combining digital image correlation technology (DICM) for deformation field monitoring can effectively improve the reliability of test results.